Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the routes for the production of phenol include a cleavage process of alkylbenzene hydroperoxide to phenol with co-production of corresponding ketones. A common route is the Hock process via cumene. This is a three-step process in which the first step involves alkylation of benzene with propylene in the presence of an acidic catalyst to produce cumene. The second step is oxidation, preferably aerobic oxidation, of the cumene to the corresponding cumene hydroperoxide (CHP). The third step is the cleavage of the cumene hydroperoxide desirably in the presence of a sulfuric acid catalyst into equimolar amounts of phenol and acetone, a co-product.
It is known that phenol and cyclohexanone can be co-produced by a variation of the Hock process in which cyclohexylbenzene is oxidized to obtain cyclohexylbenzene hydroperoxide (CHBHP), and the hydroperoxide is decomposed in the presence of an acid catalyst to the desired phenol and cyclohexanone. U.S. Pat. No. 6,037,513 discloses that cyclohexylbenzene can be produced by contacting benzene with hydrogen in the presence of a bifunctional catalyst comprising a molecular sieve of the MCM-22 family and at least one hydrogenation metal selected from palladium, ruthenium, nickel, cobalt, and mixtures thereof. The reference also discloses that the resultant cyclohexylbenzene can be oxidized to the corresponding hydroperoxide which is then decomposed to the desired phenol and cyclohexanone co-product.
It is also known that phenol and methyl ethyl ketone can be co-produced by a variation of the Hock process in which sec-butylbenzene is oxidized to obtain sec-butylbenzene hydroperoxide (SBBHP), and the hydroperoxide is cleaved in the presence of an acid catalyst to desired phenol and methyl ethyl ketone, such as that disclosed in International Publication No. WO2010/042269.
In most processes for cleavage of alkylbenzene hydroperoxide to phenol, sulfuric acid is the main catalyst. However, there are some disadvantages of using sulfuric acid for cyclohexylbenzene hydroperoxide cleavage, for example: 1) sulfuric acid is corrosive, especially in the presence of water, requiring expensive materials for reactor construction; 2) sulfuric acid needs to be neutralized before product separation and distillation, which requires additional chemicals such as phenate, caustics, or organic amines; and 3) the salt generated from neutralization requires separation and disposal, and the waste water needs to be treated.
Existing literature include numerous suggestions for replacing sulfuric acid in the cleavage of alkylbenzene hydroperoxide. For example, U.S. Pat. No. 4,490,565 discloses that zeolite beta is an effective replacement for sulfuric acid in the cleavage of cumene hydroperoxide and indicates that the yields, conversions and selectivities are advantageously superior to those produced by the use of the large pore zeolites X and Y. In U.S. Pat. No. 4,490,566, similar improvements over the large pore zeolites X and Y are reported with intermediate pore size zeolites, such as ZSM-5. International Publication No. WO 00/64849 discloses a process for producing phenol and acetone from cumene hydroperoxide is described in which the cumene hydroperoxide is contacted with a solid-acid catalyst comprising a sulfated transition metal oxide, preferably sulfated zirconia, and it is reported such a solid-acid catalyst shows a good combination of activity and selectivity as a replacement for sulfuric acid. International Publication No. WO2011/001244 discloses that cyclohexylbenzene hydroperoxide can be converted to phenol and cyclohexanone in the presence of a variety of homogeneous or heterogeneous acid catalysts selected from Brønsted acids and Lewis acids. Suitable homogeneous catalysts are said to include protic acids selected from sulfuric acid, phosphoric acid, hydrochloric acid, and p-toluenesulfonic acid. Solid Brønsted acids such as Amberlyst and Lewis acids selected from ferric chloride, zinc chloride, and boron trifluoride are also disclosed. In addition, suitable heterogeneous acids are said to include zeolite beta, zeolite Y, zeolite X, ZSM-5, ZSM-12, and mordenite. Similarly, Japan Unexamined Publication 2007-099745 discloses that cycloalkyl benzene hydroperoxides can be cleaved with high selectivity to phenol and cycloalkanone in the presence of aluminosilicate zeolites having pore diameter of 0.6 nm or greater, such as zeolite Y and zeolite beta.
It is known that molecular sieves, especially zeolites, lose performance, such as activity, selectivity, and capacity, through various deactivation mechanisms. As the molecular sieve catalyst deactivates over time, more severe conditions, such as higher temperature and/or lower through-put, are normally required to maintain comparable activity and/or selectivity. The deactivated catalyst, at the end of its useful life, may contain a significant amount of coke, such as exceeding 1 wt %, and sometimes even as high as 50 wt %.
Solid state NMR reveals that the “coke” deposited on the cleavage catalyst is a mixture of mostly oxygenates containing one or more of alcohol, ketone, carboxylic, ester or aldehyde functionalities and fused aromatic compounds. Typically, a given coke mixture can be characterized by a given H/C mole ratio, which can be determined by burning the coke using a Temperature Program Oxidation. Usually, if the H/C ratio is less than 1, the coke is considered as “hard”, otherwise it is considered as “soft”. One commonly used regeneration technique to remove “hard” coke is to burn off the coke from the catalyst in an oxidative environment, such as air or oxygen, and one commonly used regeneration technique to remove “soft” coke is use of a solvent or solvent mixture, for example, an ammonium hydroxide solution to wash the spent catalyst. However, these methods are expensive, and may result in deterioration of the catalyst due to removal of aluminum from the zeolite framework by the steam formed during calcination, as well as the alkaline washing solution. Therefore, there is a need of a method for regenerating the catalyst without deterioration of the catalyst.
U.S. Pat. No. 5,258,555 discloses a process for the preparation of a cycloalkanol by the reaction of a cycloolefin with water in the presence of a solid acidic catalyst. It also discloses that when the catalyst, e.g., the zeolite, becomes deactivated after a certain reaction time, it can be regenerated by a simple method, which desirably comprises an initial rinse of the fixed bed of solid acidic catalyst with water followed by treatment with an aqueous hydrogen peroxide solution at a temperature from 50° C. to 120° C. and preferably from 65° C. to 80° C. However, in this reference, the catalyst is used in a cycloalkane hydration reaction where water is a reactant and results in cycloalkanol as a product. On the other hand, in a cleavage process of alkylbenzene hydroperoxide to phenol, water is not a reactant in the cleavage reaction of alkylbenzene hydroperoxide to phenol, and the feed typically contains hydrocarbon, hydroperoxide, oxygenates such as organic acids, ketones and alcohols, and the resulting product typically contains a large amount of oxygenates. Consequently, the catalyst deactivation mechanism and the nature of coke formed in the hydration reaction of U.S. Pat. No. 5,258,555 would be different from that in the cleavage process of alkylbenzene hydroperoxide to phenol. Therefore, one can expect the coke formed in the cleavage process would differ substantially from the coke formed in the hydration process disclosed in U.S. Pat. No. 5,258,555. For one, it is believed that coke formed in the hydration of cycloolefin to cycloalkanol would be caused by cycloolefin, and would not contain oxygenates.
There remains a need for a method for regenerating a solid acid catalyst by which the regenerated catalyst can be recycled to a non-aqueous reaction with high catalyst activity. There is also a need for a process of producing phenol in which the deactivated catalyst can be regenerated and recycled to the process without deterioration of the catalyst.